A solid polymer fuel cell mounted on a fuel cell hybrid vehicle or the like generates electric power from a chemical reaction between a fuel gas, which contains hydrogen, and an oxidizing gas (hereinafter generically referred to as “the reactant gases”). An optimum temperature range for the fuel cell to generate electric power is generally known to be 70 to 80° C. However, the power generation by the fuel cell cannot follow a target electric power until the temperature range is reached, and there are cases where equipment (such as a motor) cannot be driven according to a request. There is also a case where it takes a long time to reach the optimum temperature range after the fuel cell is started up, depending on a use environment, such as a freezing temperature.
In view of the situations described above, the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2002-313388 is adapted to carry out low-efficiency power generation of the fuel cell when a temperature is low, thereby promptly raising the temperature of the fuel cell. The low-efficiency power generation refers to power generation which has a larger power loss, as compared with normal power generation. In other words, the low-efficiency power generation Of the fuel cell refers to power generation in which the efficiency of the power generation is set to be lower than that in the normal power generation so as to increase a self-heating value, as compared with that in the normal power generation. This fuel cell system adopts a method in which the pressure and the flow rate of the reactant gas supplied to the fuel cell are set to be insufficient in order to carry out the low-efficiency power generation.